Features

Soil Solutions

When the ancient Egyptians reinforced the steep slopes of their pyramids and the Romans stabilized their roadways, they used natural materials, including rock, fibers, fabrics and vegetation, to improve the performance and behavior of soils. But microorganisms inevitably degraded some of those additives, making civil engineering projects susceptible to ruin.

Fast forward to the 20th century. The discovery of synthetic polymers — or plastics with a wide range of properties — led to the creation of geosynthetics, giving civil engineers durable materials to mix with soils and use in and above ground, revolutionizing solutions to construction and design problems.

Geosynthetic textiles and membranes were first used in France in the 1960s to shore up earthen dams. By 1977, ASTM International Committee D13 on Textiles had formed a subcommittee on filter fabrics and later a joint subcommittee with ASTM Committee D18 on Soil and Rock to keep pace with the expanding development and applications of geotextiles and geomembranes.

“But we were crossing boundaries,” explains David Suits, executive director of the North American Geosynthetics Society, Albany, N.Y. “The textile committee members didn’t understand the concerns of the soil and rock members and vice versa.”

So in 1984, ASTM Committee D35 on Geosynthetics was formed to develop standards, test methods, guides and practices. This year, as the committee marks its 30th anniversary, it has close to 300 members representing 20 countries and oversees 155 approved standards. But applications for geosynthetics continue to expand, suggesting that the long-term potential of the industry is just beginning to emerge.

Form and Function

Geosynthetics are used with soils to achieve separation, reinforcement, filtration, drainage or containment. They’re nearly everywhere: in paved and unpaved roads, airfields, athletic fields, railroad beds, dams, drainage systems, tunnels, reservoirs, canals and landfills. They also have applications in mining, aquaculture and agriculture.

Geosynthetics fall into eight general product categories with numerous applications for each category.

Geotextiles, one of the largest groups of geosynthetics, include woven, matted, braided or knitted fabrics that can separate, reinforce, filter or drain. They’re used in dams or under roads to keep soils in place, move and channel liquids, filter out fine particles or protect and cushion geomembranes.

Geomembranes, often used in landfills, are impermeable materials that can contain liquid or gas.

Geogrids are open structures with crosspieces that reinforce roadways, retaining walls and steep slopes.

Geonets are three-dimensional structures often used in landfills or drainage areas to convey liquids. Sometimes they are used on top of geomembranes and bordered by geotextiles.

Geofoam refers to blocks that are lighter than soil and often replace heavy fill material as a base for roads, entrances to bridges and drill rigs operating on permafrost.

Geocells are three-dimensional honeycombed structures that can be filled with soil, sand, gravel or concrete to create roadways and temporary crossings over water, line channels or hold topsoil where vegetation can take root.

Geosynthetic clay liners consist of bentonite sandwiched between two geotextiles or bonded to a geomembrane to form a highly impermeable liner, usually employed in landfills.

Geocomposites refer to a combination of textiles, grids, nets or membranes.

Field Performance

As applications for geosynthetics have expanded, streamlining construction and offering more effective solutions to civil engineering challenges, Committee D35 has focused on “developing standards that give some indication of behavior and performance in the field,” says Suits, a veteran committee member and current chairman of Subcommittee D35.03 Permeability and Filtration.

“In the beginning, we looked at the basic physical properties of geosynthetics, the ability of liquid to flow through geosynthetics and puncture resistance. All of our other standards graduated from there,” says Robert Mackey, who is the chairman of Committee D35. He is principal engineer for S2L, an environmental civil engineering firm in Maitland, Fla., that specializes in landfill projects.

Joel Sprague, senior engineer with TRI Environmental Inc., a testing firm headquartered in Austin, Texas, who also chairs Subcommittee D35.01 on Mechanical Properties, notes that his subcommittee has recently developed “tests that apply to stronger geosynthetics where it’s critical that they provide long-term engineered performance, so they can be used in reinforced soil and pavement applications.” Similarly, adds Suits, “ASTM standards have been crucial to getting geomembranes approved for use in landfill areas.”

Also, since plastic stretches and can deteriorate with outdoor exposure, the development of accelerated testing methods to determine how geosynthetics can hold up to functional and environmental stress over time — particularly the stepped isothermal method that determines long-term creep (or connection strength displacement) characteristics in a short period of time — “has been fundamental to taking the industry from the low-tech to the high-tech use of geosynthetics. It’s revolutionized the industry,” says Sprague.

Subcommittee D35.02 on Endurance Properties has developed 24 standards having to do with everything from the mechanical hydraulics to the durability of geosynthetics. For example, before the development of ASTM D5397, Test Method for Evaluation of Stress Crack Resistance of Polyolefin Geomembranes Using Notched Constant Tensile Load Test, poor quality resins in geomembranes resulted in field failures. “Our standard virtually eliminated those resins from the market,” says D35.02 chairman George Koerner, director of the Geosynthetic Institute in Folsom, Pa.

Other standards that have had a significant impact on the industry include ASTM D7238, Test Method for Effect of Exposure of Unreinforced Geomembrane Using Fluorescent UV Condensation Apparatus, which allows geomembranes to be evaluated for exposed applications, thereby ensuring the safety of such uses. Likewise, ASTM D4355, Test Method for Deterioration of Geotextiles by Exposure to Light, Moisture and Heat in a Xenon Arc Type Apparatus, offers a way to assess the lifetime of exposed geotextiles.

Providers and Users

In addition to civil engineers and builders, ASTM International standards on geosynthetics are used by manufacturers, the military and regulatory agencies, including the U.S. Department of Transportation. In fact, under a national transportation product evaluation program sponsored by the American Association of State Highway and Transportation Officials, domestic and foreign manufacturers — including those in India, Vietnam, Saudi Arabia, France and China — who supply geosynthetics to the DOT, must meet ASTM standards, making the standards globally relevant.

Currently, mining has surpassed the waste management industry as the largest user of geosynthetics. For example, copper and gold mining operations, particularly in Latin America and South Africa, are heavy users of geomembranes to contain mountains of ore. In the United States, the explosion of hydraulic fracturing has boosted the use of geosynthetics to contain fracking fluids and backwash at drill sites, among other uses.

New Products and Applications

The need for new geosynthetic standards has hardly slowed. “We always come up with better methodologies to test materials and new test methods that are more applicable to geosynthetic materials,” says Mackey. For example, standards for geogrids are becoming increasingly important since they’re used in uniaxial applications, such as walls and levies, and multiaxial applications, such as roads. “We need to know their low strain tensile and interaction properties as well as the appropriate properties of grids with unique geometries,” notes Sprague.

Plus, the number of new geosynthetics or geosynthetic applications hasn’t abated, requiring new tests and standards for manufacturers that lend validity to their products and that provide information to users.

“We actually joke about the geosynthetic of the day,” says Koerner. Among new products and combinations of materials are concrete powder sandwiched between geotextiles that can be rolled out, moistened and hardened into shape; gel-infused geotextiles and super-absorbent geosynthetic clay liners; geosynthetic mats for erosion control; geotextiles coated with molten polymer that can be used as temporary roofs; and geotextiles of one or more acres in size that can be rolled out to provide wide-area surface impoundments for, say, a fracking site.

ASTM Committee D35 on Geosynthetics currently has 19 new standards under development. They address mechanical and endurance properties, such as the draft WK36264, Test Method for Determining Long-Term Connection Strength Displacement (Creep) Between Geosynthetic Reinforcement and Segmental Concrete Units (Modular Concrete Blocks), a test protocol that will help determine the interaction between the visible facing of a wall and the reinforcement strength of the geosynthetic that reaches back into the soil. Other geosynthetic applications that will benefit from new standards include leak location, pavement reinforcement, and geotextile and filter systems.

Future Applications

Even now, geosynthetics are being employed or considered for what Koerner dubs “Buck Rodgers-type applications” that extend far beyond traditional civil engineering uses. Among the newer applications for geosynthetics are odor control barriers; translucent bags for growing algae to produce biofuels; tube-like devices for evacuating high-rise buildings; and liners and jackets equipped with electric sensors for detecting leaks in pipelines.

“More change is on the horizon,” Koerner says. And what we now consider geosynthetics may eventually have yet another name and possibly even another ASTM International committee to develop new standards and test methods in the future.

Adele Bassett is a freelance writer who has covered everything from youth gangs in Colorado to earthquakes in Connecticut while working for a variety of corporations and publications. She holds a B.A. in English, an M.S. in journalism and an M.B.A.